Allergic reactions to food represent a major and growing medical, social and economic problem worldwide. Up to 6% of small children and 3 to 4% of the adults have a confirmed allergic reaction to basic foods. Eight types of food account for over 90% of allergic reactions; milk, eggs, peanuts, tree nuts, fish, shellfish, soy and wheat [1, 2]. The clinical reactions of allergy vary from minor oral reactions with itch and mucosal swelling, to urticaria and angioedema, gastrointestinal symptoms, asthma and anaphylaxis with possible fatal result [3]. The economic costs of allergy in the USA alone are estimated to be USD 14.5 billion per year, with food allergies costing USD 500 million per year [4].
Shellfish allergy is a potentially life-threatening disease that is seldom outgrown [1; 2] and, in some parts of the world, the most common food allergy among adults [3]. Among crustaceans, such as shrimp, crab, crawfish and lobster, shrimp is frequently identified as a cause of IgE mediated adverse reactions in food allergic individuals. Although exact numbers on the prevalence of shrimp allergy are lacking, estimations have ranged from 0.6 to 2.8% in food allergic individuals [5, 6]. The shellfish species that most frequently elicit food-allergic reactions belong to the taxonomic class Crustacea that includes shrimp, crab, crawfish and lobster. Affected individuals usually display allergic reactivity to multiple crustacean species. Molecular and clinical cross-reactivity was reported between crustaceans and other invertebrate foods such as mussels, oyster, squid and octopus, but also to invertebrate aeroallergens such as house dust mite and cockroaches (Reviewed by Lopata et al., 2010) [1].
The presence of a heat-stable allergen in shellfish was first identified in shrimp by Hoffman et al. (1981) [4] and this allergen was later identified as the muscle protein tropomyosin [5-7]. More than 80% of shrimp-allergic individuals were reported to have serum IgE against shrimp tropomyosin [6; 8-10]. The amino acid sequence of invertebrate tropomyosins is highly conserved, with 95% identity between shrimp and Storage mite (Tyrophagus putrescentiae). Tropomyosin was found to play an important role in the cross-reactivity seen between the different invertebrate species—suggesting tropomyosin to be an invertebrate pan-allergen [1].
The most common control of food allergy is merely avoidance of the relevant offending allergen, i.e. no vaccine is available for the treatment of food allergy. For venom and inhalant allergies, and grass and birch in particular, desensitisation and tolerance development has been carried out for almost 100 years as subcutaneous or recently sub-lingual immunotherapy (SCIT and SLIT, respectively) [7]. Treatment involves increasing doses of standardised allergen extracts until a maintenance dose is reached; this dose is injected approximately every second month for 3-5 years. Alternative strategies are currently being tried out, such as intra-lymphatic injections, which may considerably shorten the time of treatment, but such treatment is experimental at present [8]. Due to safety reasons, tolerance induction in the form of SCIT has been abandoned in food allergic patients.
Another treatment that is used today is Omalizumab (trade name XOLAIR®, Roche/Genentech and Novartis) which is an injectable, prescription medicine approved for patients 12 years and older with moderate to severe allergic asthma in the United States and with severe, persistent allergic asthma in many other countries. It is a recombinant DNA-derived humanized monoclonal antibody and exerts its action by binding to circulating IgE, reducing IgE receptor expression, and decreasing mediator release from mast cells and basophils [9]. Omalizumab has also been studied in combination with allergen-based SIT for the purpose of reducing anaphylactic reactions and to achieve therapeutic effects in shorter treatment periods. However, Omalizumab does not comprise allergen specific immunotherapy as opposed to the presently proposed invention.
Fibrinogen-like protein 2 (FGL2), also known as fibroleukin, is a 70-kDa glycoprotein that belongs to the fibrinogen-related superfamily of proteins [10]. It is expressed on the surface of macrophages, T cells and endothelial cells and exerts in that form (as a transmembrane protein) prothrombinase activity [11]. The prothrombinase activity of FGL2 has been associated with several diseases such as hepatitis and abortion [12]. However, as a soluble protein FGL2 lacks prothrombinase activity has instead been associated with immune-suppression by binding to the inhibitory receptor FcgammaRIIb (FcγRIIb) [13] that is highly expressed on the cell-surface of B-cells and basophils/mast cells. Soluble FGL2 is secreted mainly by memory T-cells and was recently presented as a marker for tolerance induction [14].
Human basophils express high-affinity IgE receptors (Fcepsilon RI, FcεRI). FcεRI is associated with two immunoreceptor tyrosine-based activation motifs (ITAM) that are activated upon FcεRI aggregation, when specific antigens (Ag) binds to receptor-bound IgE antibodies. Activated basophils release vasoactive mediators and cytokines that promote allergic inflammation [15].
Human and mouse mast cells, basophils and B-cells express the inhibitory receptor FcγRIIb on the cell surface [16, 17]. FcγRIIb is an immunoreceptor tyrosine-based inhibition motif (ITIM) containing inhibitory receptor. Co-engagement of FcγRIIb with FcεRI on basophils [16] and mast cells [18] inhibits IgE induced activation of these cells. Furthermore, co-engagement of FcγRIIb and B-cell receptor complex has been shown to supress ex-vivo B-cell activation and humoral responses in vivo [19].
WO 97/07218 describes fusion proteins comprising one or more antigens and one or more moieties interacting with human FcγRII. The invention relates to complexes of human IgG and antigen/allergen and concerns fusion proteins between anti-CD32 molecules and antigen/allergen.
U.S. Pat. No. 7,632,495 B2 and US2010/0048486 A1 describes methods and compositions for inducing immune suppression in graft rejection and autoimmune diseases by administering an effective amount of a soluble FGL2 protein or a nucleic acid encoding a soluble fgl2 protein.
U.S. Pat. No. 7,655,229 B2 describes antibodies that selectively bind human FcγRIIb, with little or no binding to other human FcgammaRs. The inventions provides isolated bispecific antibodies comprising an antibody that selectively binds FcγRIIb, and a second antibody that specifically binds an activating receptor for inhibiting immune responses and suppressing histamine release.
US2006/0171942 describes fusion molecules comprising an Fcε fragment sequence including functionally active CH2, CH3 and CH4 domains of the constant region of an IgE heavy chain linked at its C-terminus to the N-terminus of a second polypeptide including functionally active hinge, CH2 and CH3 domains of the constant region of an IgG1 heavy chain for the treatment of allergic disease.
There is thus an urgent need to develop means and methods for a vaccine against food allergy such as shrimp allergy. Accordingly, the present invention provides means and methods to address such needs and interests for food allergy, and particularly shrimp allergy.